The aim of this program is to develop a low-cost, easy-to-use instrument to measure the blood flow in artificial dialysis access grafts. With such an instrument, these grafts could be monitored at frequent enough intervals to detect the falling flow levels that predict graft failure. Such graft failure is a major medical problem for the 250,000 Americans who undergo hemodialysis. The proposed instrument will utilize a new kind of ultrasound transducer, the diffraction-grating transducer, in a special Doppler technique that eliminates the need for imaging the graft during measurement, and is especially suitable for by minimally skilled operators. An early version of this instrument has shown promise in measuring dialysis access graft flow, and has proven that the range of normal physiological variation in graft flow is small enough that the proposed flow measurements should reveal impending graft failure. In the Proposed Phase I of this project, a prototype of the desired instrument will be constructed and its accuracy and ease of use validated in clinical use by comparison with standard flow techniques in a small number of hemodialysis patients. With the feasibility of the instrument so demonstrated, Phase II would continue with construction of a number of such instruments to be used in a multi-center trial to prove that their use can extend the life of artificial dialysis grafts. The economic benefit of such graft life extension can approach a billion dollars a year, ensuringcommercialization of the instrument.